Two activists with the EU flag and Union Jack painted on their faces kiss each other in front of Brandenburg Gate to protest against British exit from the European Union, in Berlin on Sunday. The sign reads, 'A kiss against hate.'

Paris — The scene is an airplane flight over Europe “in the near future”; an archeologist turns to the girl seated next to him and tells her that he’s going to be late to his lecture on the European Union.

“What’s that?” she asks earnestly.

And so begins the docudrama "The Great European Disaster," aired recently at Paris’s Maison de L’Europe. Taking the audience into an era that sees United Kingdom Independence Party (UKIP) leader Nigel Farage as Britain’s prime minister, National Front’s Marine Le Pen as French president, and the self-declared Islamic State advancing into Europe, it was panned by anti-EU forces as fear-mongering.

“Everyone is looking at London,” says Gian Paolo Accardo, the executive editor of VoxEurop, who fielded questions from the audience. “The whole union is suspended by what is going to happen in the United Kingdom.”

A vote to leave the EU will change the future direction of Britain most dramatically. But the rest of Europe could lose a military leader, a diplomatic heavyweight, a counterweight to Germany – and its political mooring.

While the EU has faced a constant stream of crises testing its viability, a Brexit would represent its first concrete step backward. After the refugee crisis last summer, the border-free Schengen area threatened to implode, though it survived intact. During the sovereign debt crisis, leaders rushed to keep Greece in the eurozone to stop a wider fallout. The zone also survived.

But losing a member state could start a process of irreparable reversal, undermining the foundation of the post-war project. And as Europeans stand at the brink, they are trying to plead their case for Britain to stay while reckoning with the shortcomings that have led to a wider Western backlash against globalization and the political status quo.

“It feels a lot bigger [now] because back then, [the debt crisis] was seen mainly as a moment where we had to fix some of the system, fix some of the hardware. It was more of a technocratic problem,” says Sylke Tempel, editor-in-chief of Internationale Politik, published by the German Council on Foreign Relations. “It is not anymore about fixing the structure of the European Union; it is fixing the soul of the European Union.”

A chain reaction?

Britain has always been a prickly member of the EU. A latecomer to the bloc that joined only because of its economic woes of the 1970s, its ties to the EU have been transactional, not emotional. It never signed up to use the euro, nor does it belong to Schengen, and Euroskepticism has always run through it.

Still, even just six months ago, few in Europe thought they'd find themselves watching Britain on the cusp of leaving, with polls too close to call just days ahead of the vote.

One of the most concrete repercussions could be that other referendums are organized. Euroskepticism is growing throughout the bloc. According to a study by the Pew Research Center that polled attitudes in 10 countries, only 51 percent of respondents said they hold positive views of the EU. That number is just 44 percent in the UK. It is the second lowest in France, with 38 percent feeling positive, ahead only of debt-battered Greece.

Speaking to journalists ahead of the vote, Herve Mariton, who is running for the center-right presidential ticket in France, says that he would expect the French to clamor for a similar vote in the case of a Brexit – and as it stands now, he says he is not confident a remain vote could win. The French had already voted in 2005 against a treaty establishing a constitution for Europe. Since then, Ms. Le Pen’s National Front, which advocates for leaving the euro, has grown, poised to make it to round two of the 2017 president race.

“There will be the urge for a referendum, and we should anticipate it from a French point-of-view and a pan-European point-of-view,” Mr. Mariton says.

A new balance of power

Even if the referendum doesn’t create a domino effect, the absence of Britain from the EU would shift the balance of power in Europe. France would lose the only other member with a serious defense and security culture. Germany would lose the bloc’s most significant market-friendly member, and would become even more dominant.

“We lose a counterbalance to too much Continental power. And with a weak France and a turning-inward Poland, it gives too much power to Germany,” says Dr. Tempel.

Not only is Germany uncomfortable with that power, but its chancellor, Angela Merkel, would be made more vulnerable to critics who say she is bullying Europe – a charge that echoes from debt-stricken countries in the south that are angry at austerity policies to disgruntled members in the east furious about refugees.

Perhaps no one is paying more attention than the British expatriates. Many are worried about their pensions, right to work abroad, and the direction their native country is taking. Richard Frackowiak, a retired neurologist in France, says he considers his kin the typical European family: roots in Poland, work experience around the bloc, children around the globe.

“We are truly Europeans as are most people living in the countries of Europe,” he says. “I think Britain will suffer hugely if we leave.”

If Brits vote to remain, he’ll obviously not be the only one to sigh relief. Political leaders, international bodies, and pro-EU advocates across the block are urging Brits to stay.

At a conference ahead of the vote, German Foreign Minister Frank-Walter Steinmeier was quoted by the Financial Times as saying: “If it really comes to Great Britain leaving, then the EU will find itself in a deep crisis.”

'We have to move on'

Leaders are adopting some of the apocalyptic tone of "The Great European Disaster," threatening an unforgiving response if Britain pulls out, including lengthy processes for new trade deals.

Still, frustration is also growing with Britain, says Mr. Accardo, the vice president of the French section of the Association of European Journalists, and at a referendum that is seen as a bet by Mr. Cameron that he has badly handled.

“This has taken a lot of political, journalistic, and mental energy from European countries, while there are issues that are far more important to tackle, like unemployment or competitiveness,” he says. “We have to move on.”

“It’s a very significant moment in time,” says Janis Emmanouilidis, director of studies at the European Policy Center in Brussels. No matter what happens, this week will prove to be perhaps the biggest wake-up call the bloc has gotten.

“Given the state of affairs in the EU, there is a need to be honest and have an honest debate about where we stand and what needs to be done.”